1. Field of Invention
The invention relates to a rotating periodic color-regulating module of the image display device for regulating the color of a light beam. More particularly, the invention relates to a rotating periodic color-regulating module that can improve the usage of light.
2. Related Art
The image display device is used to project an image on a screen for display or teaching purposes. The image display device uses a picture generation device to produce all kinds of images. It has to provide beams of light with rapid and periodic color changes in order to form a color picture. Therefore, most of the image display devices utilize the design of a color wheel to satisfy such a requirement.
The color wheel is composed of a plurality of color filters, by which light is filtered to allow only a monotonic color beam to pass. The color wheel is rotating in such a way that the color filters are rotated to the optical path to provide beams of light with rapid and periodic color changes. Since it needs a rotating color wheel to change colors, the color filters are often made in wedge shapes and attached on a substrate to form the color wheel. The color wheel is then installed on a motor.
However, a generic problem with the color wheel is that the usage efficiency of light is fairly low. This is because the color wheel is generally composed of red (R), green (G) and blue (B) filter thin films and blank parts. The R, G and B colors have equal areas and occupy 85% of the total area. The rest part is blank. When a beam of light passes through places without a color thin film, all colors of light can pass through. However, when the beam of light passes through the red color thin film, all colors of light will be filtered away except for the red light. Therefore, only one third of light can pass. Analogously, the green and blue filter thin films work in the same way. Excluding the 15% blank area, optical energy that can pass through the color wheel is roughly 40% of the original optical energy emitted. Considering the optical loss, the true optical energy that can be used is only slightly more than 30%.
This is an essential point that the efficiency of the image display device cannot be increased. Although some method had been proposed to solve the problem, they either cost too much or involve complicated and difficult process in manufacturing.
In view of the above-mentioned problems, the invention provides a rotating periodic color-regulating module of the image display device, which can increase the usage of light but does not increase the manufacturing cost.
According to the disclosed module, a mirror is provided on the entering place of light to reflect light reflected by the color filters on the color wheel. This can effectively increase the usage of light.
To increase the light use, a grating element is installed at the entering place of light. When a beam of light passes the grating element, it is split into several beams of light according to different wavelengths moving toward the corresponding filters. This further increases the percentage of light that passes through the color wheel. A color separating light guide is installed after the filter so that light is guided to emit homogeneously. Although such a method can increase the usage of light, it cannot be directly applied to image display devices because they need beams with color changed rapidly and periodically in order to convert them into images.
Therefore, a color-regulating module is provided at the light output place. It is a polygonal prism, which is mounted on a rotating motor to rotate. When a beam of light passes through the prism, it is deflected by an angle due to the different refraction indices between the prism and the air. Light of different wavelengths will be deflected by different angles too. As the prism rotates to a specific angle, light will greatly change its deflection angle and therefore the outgoing beams. With the combination of a high-speed rotating prism and the above-mentioned homogeneous light, beams of light with rapidly and periodically color changes can be provided to an image display device. Therefore, the disclosed module does not only increase the use of light, but has a simple structure that allows mass production at a lower cost.